[Clang][Sema] Remove invalid ctor (NFC) (#82161)

`TemplateArgumentLocInventIterator` default constructor should not
exists

https://github.com/llvm/llvm-project/blob/3496927edcd0685807351ba88a7e2cfb006e1c0d/clang/lib/Sema/TreeTransform.h#L4742
because it doesn't and couldn't initialize `Self` member that is
reference:

https://github.com/llvm/llvm-project/blob/3496927edcd0685807351ba88a7e2cfb006e1c0d/clang/lib/Sema/TreeTransform.h#L4721-L4723

Instantiation of this constructor is always a compile-time error. 

Please note, that I didn't run any tests, because cannot imagine
situation where this constructor can be properly used. There are no new
tests for this fix for the same reason.

clang/lib/Sema/TreeTransform.h

@@ -4759,8 +4759,6 @@ class TemplateArgumentLocInventIterator {
     const TemplateArgumentLoc *operator->() const { return &Arg; }
   };
 
-  TemplateArgumentLocInventIterator() { }
-
   explicit TemplateArgumentLocInventIterator(TreeTransform<Derived> &Self,
                                              InputIterator Iter)
     : Self(Self), Iter(Iter) { }